For the production of polyurethane foams, polysiloxane-polyoxyalkylene block copolymers, which enable a uniform pore structure to be formed and stabilize the foam formed up to the end of the reaction, are added to the reaction products. However, not all polysiloxane-polyoxyalkylene block copolymers are equally suitable. In order to be useful as polyurethane foam stabilizers, the polyoxyalkylene blocks and the polysiloxane block of the block copolymers must be present in a well-balanced ratio. Moreover the structure of the two blocks is also of great importance. For the structure of an as effective a foam stabilizer as possible, there is a plurality of variables for the polyoxyalkylene block as well as for the polysiloxane block.
The polyoxyalkylene block may be composed of different oxyalkylene units, particularly of oxyethylene, oxypropylene and oxybutylene units. Moreover, the ratio by weight of these units to one another, as well as the molecular weight of the polyoxyalkylene block can be varied. The end group of the polyoxyalkylene block, which can be a reactive group (such as an OH group), or inert (such as an alkoxy group) with respect to the polyurethane formation, is also of importance. The polyoxyalkylene block can be linked to the polysiloxane block by a hydrolytically stable C-Si bond or by the hydrolytically less stable C-O-Si bond. Furthermore, different polyoxyalkylene blocks can also be linked to the polysiloxane block.
The polysiloxane block can be varied with respect to the nature and proportion of the silicon units. The siloxane block can be linear or branched and have different molecular weights. The polyoxyalkylene blocks can be linked terminally and/or laterally to the polysiloxane block.
The effectiveness of a polysiloxane-polyoxyalkylene block copolymer as a foam stabilizer can be predicted only to a limited extent. The expert is therefore required to investigate the possible variations largely empirically. In view of the large, almost indeterminable number of possible variations, the finding of special variation possibilities and corresponding block copolymers represents a progressive and thus inventive effort.
Polysiloxane-polyoxyalkylene block copolymers, which have different polyoxyalkylene groups in the average molecule, have already been described in numerous publications. Of the large number of corresponding publications, the following are named as being representative:
German Patent 15 70 647: Chloropolysiloxanyl sulfates are reacted with mixtures of alkylene oxide adducts, which consist of
50 to 95 OH-equivalent percent of polyalkylene glycol monoethers, which consist of ethylene oxide and propylene oxide units and contain 40 to 70% by weight of oxypropylene units and have a molecular weight of 1,000 to 3,000 and the hydroxyl groups of which preferably are secondary, and PA1 5 to 50 OH-equivalent percent of alkylene oxide adducts of multihydric hydroxyl compounds having a molecular weight of 130 to 3,500, the polyalkylene glycol component of which consists of ethylene oxide and/or oxidepropylene units and which have an OH equivalent weight of up to 1,750 and the hydroxyl groups of which are predominantly secondary, PA1 25 to 70% by weight of a polyoxyalkylene with an average molecular weight of 1,600 to 4,000 and an ethylene oxide content of 20 to 100% by weight, the remainder being propylene oxide PA1 30 to 75% by weight of a polyoxyalkylene with an average molecular weight of 400 to 1,200 and an ethylene oxide content of 65 to 100% by weight, the remainder being propylene oxide and optionally higher alkylene oxides.
the ratio by weight being selected so that there is at most 1.4 and preferably 1.05 to 1.2 OH equivalents per acid equivalent of the chloropolysiloxanyl sulfate.
German Patent 16 94 366: Those polysiloxane-polyoxyalkylene block copolymers are used as foam stabilizers, the polysiloxane block of which is built up in a known manner and the polyoxyalkylene block of which, however, consists of
and optionally higher alkylene oxides, and
German Offenlegungsschrift 25 41 865: The polysiloxane-polyoxyalkylene block copolymers are defined with respect to their polyoxyalkylene block so that the one polyoxyalkylene block has an average molecular weight of 900 to 1,300 and consists of up to 30 to 55% by weight of ethylene oxide, the remainder being propylene oxide, and the other polyoxyalkylene block has an average molecular weight of 3,800 to 5,000 and consists of 30 to 50% by weight of ethylene oxide, the remainder being propylene oxide.
European Publication 0 275 563: The block copolymer, described in this published European patent application, comprises three different polyoxyalkylene blocks, namely a block, which contains 20 to 60% by weight of oxyethylene units and has a molecular weight of 3,000 to 5,500, a further block with 20 to 60% by weight of oxyethylene units and a molecular weight of 800 to 2,900 and a third block which consists only of polyoxypropylene units and has a molecular weight of 130 to 1,200.